Rudists: Extreme climate witnesses

PUBLICATION — de Winter, N. J., al Fudhaili, N., Arndt, I., Claeys, P., Fraaije, R., Goderis, S., Jagt, J., López Correa, M., Munnecke, A., Stolarski, J., and Ziegler, M. 2025. Living on the edge: Response of rudist bivalves (Hippuritida) to hot and highly seasonal climate in the low-latitude Saiwan site, Oman. Climate of the Past 21, 2361–2387, doi:10.5194/cp-21-2361-2025

Figure: Variability in temperature measured in different species of rudist bivalves (upper plot) and well preserved specimen of Vaccinites vesciculosus (lower photo). Coloured violin plots indicate the spread in the full dataset, while black symbols indicate monthly mean values. Grey horizontal lines show the highest and lowest monthly mean value, respectively, through the entire dataset.

Tropical temperature swings from 75 Million years ago
Rudists, extinct bivalves with massive shells,  built vast reefs in the tropical Cretaceous seas. Clumped-isotope analyses of well-preserved shells from Oman, were used to reconstruct seawater temperatures from 75 million years ago. The climate showed strong seasonality, from relatively cool winters around 20 °C to summers above 40 °C. Some rudists stopped growth during these extremes. The study shows how ancient marine life coped with intense greenhouse conditions.